The present invention generally relates to the electrical connection of two elements and, more particularly, to the preferably solderless connection of two preferably like metallic elements, preferably using an optical fiber that holds the electrical elements in contact while directing a laser emission to the location to be bonded.
Thermal inkjet print cartridges operate by rapidly heating a small volume of ink to cause the ink to vaporize and be ejected through one of a plurality of orifices so as to print a dot of ink on a recording medium, such as a sheet of paper. The properly sequenced ejection of ink from each orifice causes characters or other images to be printed upon the paper as the printhead is moved relative to the paper.
An inkjet printhead generally includes: (1) ink channels to supply ink from an ink reservoir to each vaporization chamber proximate to an orifice; (2) a metal orifice plate or nozzle member in which the orifices are formed in the required pattern; and (3) a silicon substrate containing a series of thin film resistors, one resistor per vaporization chamber.
To print a single dot of ink, an electrical current from an external power supply is passed through a selected thin film resistor. The resistor is then heated, in turn superheating a thin layer of the adjacent ink within a vaporization chamber, causing explosive vaporization, and, consequently, causing a droplet of ink to be ejected through an associated orifice onto the paper.
In U.S. application Ser. No. 07/862,668, filed Apr. 2, 1992, entitled xe2x80x9cIntegrated Nozzle Member and TAB Circuit for Inkjet Printhead,xe2x80x9d a novel nozzle member for an inkjet print cartridge and method of forming the nozzle member are disclosed. This integrated nozzle and tab circuit design is superior to the orifice plates for inkjet printheads formed of nickel and fabricated by lithographic electroforming processes. A barrier layer includes vaporization chambers, surrounding each orifice, and ink flow channels which provide fluid communication between an ink reservoir and the vaporization chambers. A flexible tape having conductive traces formed thereon has formed in it nozzles or orifices by excimer laser ablation. By providing the orifices in the flexible circuit itself, the shortcomings of conventional electroformed orifice plates are overcome. The resulting nozzle member having orifices and conductive traces may then have mounted on it a substrate containing heating elements associated with each of the orifices. Additionally, the orifices may be formed aligned with the conductive traces on the nozzle member so that alignment of electrodes on a substrate with respect to ends of the conductive traces also aligns the heating elements with the orifices. The leads at the end of the conductive traces formed on the back surface of the nozzle member are then connected to the electrodes on the substrate and provide energization signals for the heating elements. The above procedure is known as Tape Automated Bonding (xe2x80x9cTABxe2x80x9d) of an inkjet printhead assembly, or TAB Head Assembly, (hereinafter referred to as a xe2x80x9cTHAxe2x80x9d)
An existing solution for connecting the conductive traces formed on the back surface of the nozzle member to the electrodes on the substrate for a THA requires a flexible TAB circuit with a window in the Kapton tape. This window provides an opening for the bonder head, which permits direct contact of the thermode (single point or gang) with the TAB leads. Therefore, the attachment process is performed without direct contact between the thermode and Kapton tape. A TAB bonder thermode comes in direct contact with the flex circuit copper TAB leads through this window. The thermode provides the thermal compression force required to connect the TAB conductive leads to the printhead substrate electrode. Alternatively, an ultrasonic method may be used to connect the TAB conductive leads to the printhead substrate electrode. This window is then filled with an encapsulation material to minimize damage to the conductive leads, shorting, and current leakage. This encapsulation material may flow into the nozzles and cause blockages. Therefore, the Tab Head Assembly (xe2x80x9cTHAxe2x80x9d) is designed in a manner that allows a 0.50 to 0.75 mm gap between the edge of the encapsulation and the nozzles. This increases the substrate size by 1 to 1.5 mm. The encapsulation material also creates an indentation that is not desirable for serviceability, and creates coplanarity, and reliability problems.
Accordingly, it would be advantageous to have a process that eliminates the need for a window in the TAB circuits. The elimination of the window would result in elimination of the need for an encapsulation material to cover the conductive leads in the TAB circuit. This in turn would result in die size reduction, (or increased number of nozzles with the same die size), ease of assembly, higher yields, improved reliability, ease of surface serviceability, and overall material and manufacturing cost reduction.
The present invention provides a method for the solderless electrical connection of two contact elements by using a laser light beam attached to a fiber optic system which directs the light to the spot to be bonded. Through use of a fiber optic system the laser beam is optimally converted into thermal energy, and bad connections due to underheating or destruction of the contacts due to overheating do not occur. The method and apparatus provide rapid, reproducible bonding even for the smallest of contact geometries. For example, the method of the invention results in solderless gold-to-gold compression bonding of conductive leads contained in a polymer flex circuit tape, such as a polyimide, without damaging the tape. A strong solderless gold to gold bond can be formed between the gold-plated copper lead on the flex circuit tape and a gold-plated pad on a semiconductor chip without the need for a window in the flex circuit and without any damage to the tape.
In the application of the present invention to the bonding of conductive leads on TAB circuit to the silicon substrate of an inkjet printhead the need for a window in the TAB circuit is eliminated. The elimination of the window results in elimination of the need for an encapsulation material to cover the conductive leads in the TAB circuit. This in turn results in die size reduction, (or increased number of nozzles with the same die size), ease of assembly, higher yields, improved reliability, ease of nozzle serviceability, and overall material and manufacturing cost reduction.
While the present invention will be described, for purposes of illustration only, in conjunction with the bonding of conductive leads on a TAB circuit to the silicon substrate of an inkjet printhead, the present method and apparatus for the solderless electrical connection of two contact elements by using a laser light beam attached to a fiber optic system is applicable to bonding any electrical members to each other.
Other advantages will become apparent after reading the disclosure.